The introduction of copper (Cu) metal into multilayer metallization schemes for manufacturing integrated circuits can necessitate the use of diffusion barriers/liners to promote adhesion and growth of the Cu layers and to prevent diffusion of Cu into the dielectric materials. Barriers/liners that are deposited onto dielectric materials can include refractive materials, such as tungsten (W), molybdenum (Mo), and tantalum (Ta), that are non-reactive and immiscible in Cu, and can offer low electrical resistivity. For example, Cu integration schemes for technology nodes less than or equal to 130 nm can utilize a low dielectric constant (low-k) inter-level dielectric, followed by a physical vapor deposition (PVD) Ta layer or a TaN/Ta layer, followed by a PVD Cu seed layer, and an electro-chemical deposition (ECD) Cu fill. Generally, Ta layers are chosen for their adhesion properties (i.e., their ability to adhere on low-k films), and TaN/Ta layers are generally chosen for their barrier properties (i.e., their ability to prevent Cu diffusion into the low-k film).
More recently, other materials, such as ruthenium (Ru) and rhodium (Rh) have been identified as potential barrier and seed layers since they are expected to behave similarly to conventional refractory metals. In one example, Ru or Rh layers can be deposited onto Ta/TaN layers. However, it is possible that the use of Ru or Rh can permit the use of only one barrier layer, as opposed to two layers, such as Ta/TaN. For example, it is possible that a Ru layer can replace the Ta/TaN barrier layer. Moreover, current research is finding that a Ru layer can further replace the Cu seed layer, and bulk Cu fill can proceed directly following Ru deposition.
Ru layers can be deposited from a ruthenium-containing precursor, such as a ruthenium carbonyl precursor or a ruthenium organometallic precursor. However, Ru deposition processes can suffer from low deposition rates due to the low vapor pressures of a number of ruthenium precursors and the transport issues associated therewith, thereby making deposition of Ru layers impractical even if the deposition provides good step coverage over high-aspect-ratio features. On the other hand, Ru deposition processes with high enough deposition rates for manufacturing can suffer from unacceptable step coverage over high-aspect-ratio features. Overall, the inventors have observed that new Ru deposition processes are needed that can provide high deposition rates and desired step coverage over high-aspect-ratio features.